US Patent 7418860 Ultrasonic fluid level sensor

A fluid level sensor for determining a fluid level within a container, includes a transducer for generating sonic or ultrasonic waves and a wave guide. The wave guide has a first end operatively coupled to the transducer and a second end for immersion into the fluid, the second end spaced a predetermined distance from the first end, wherein a gap is formed between the first end and the second end. The sensor can be used to measure a fluid level using both an impedance mismatch signal and a fluid conductance signal.